The Novel Insertion of Imines into a Late-Metal−Carbon σ-Bond:  Developing a Palladium-Mediated Route to Polypeptides

Abstract

The palladium complex (bipy)Pd(CH 3 )NCC-H 3 + OTf -(2; bipy ) 2,2′-bipyridyl, OTf ) OSO 2 CF 3 ) has been found to undergo the novel sequential insertion of carbon monoxide and imine into the metal-carbon bond in a manner directly analogous to that observed in olefin/CO alternating copolymerizations. The structure of the insertion products, (bipy)Pd[C(Tol)HNRCOC-H 3 ] + OTf -, suggests that the unique combination of CO insertion, amide bond formation, carbonyl oxygen chelation, and resonance stabilization of the chelate ring provides the stabilization required for imine insertion to occur. a Measured by 1 H NMR at 30°C for 3a-d + CD3CN T 2 + 1a-d. b From plot of Keq vs 1/T from 25 to 75°C.

Metal‐Catalyzed Synthesis of Alternating Copolymers

“…Since the reaction is analogous to olefin/CO copolymerization, the possibility for imine/CO copolymerization has been investigated by using palladium catalysts that have been widely used in olefin/CO copolymerization over the past decade. In 1998, Arndtsen and coworkers [79] and Sen and coworkers [80] reported the first observation of imine insertion into acyl carbon-palladium bonds. This achievement represented a critical step toward metal-catalyzed copolymerization of imines and CO. By using diphosphine and bipyridine as ligands, Sen and Arndtsen observed the coordination of the imine through its nitrogen atom (30), (Scheme 7).…”

Imines in Stille‐Type Cross‐Coupling Reactions: A Multicomponent Synthesis of α‐Substituted Amides

“…[11,12] 3 (dba = dibenzylideneacetone) leads to the quantitative formation of chelated product 1'. Notably, the 1 H NMR spectrum reveals reduction of the imine C = N bond upon addition to palladium (d = 5.06 ppm (s, CHTol)), and 13 C NMR data indicates that amide chelation has occurred to form a five-membered metallacycle (d = 182.3 ppm (COPh)). [13,14] Mass spectrometric data is consistent with the dimeric structure of 1', likely formed through bridging chloro ligands to generate a pseudo-square-planar 16-electron palladium complex.…”

Cobalt‐Catalyzed Carbonylation of N‐Alkylbenzaldimines to ‘N‐Alkylphthalimidines’ (= 2,3‐Dihydro‐1H‐isoindol‐1‐ones) via Tandem CH Activation and Cyclocarbonylation

“…To probe this mechanism, the deuterated benzaldimines 3 with CO by 13 C-NMR and GC/MS showed that 80% of the product had a CHD methylene unit, while 20% possessed a CH 2 unit (Scheme 5). In the case of the reaction of C 6 3 with CO, a similar analysis showed that 70% of the product contained a CD 2 unit, whereas 30% showed a CHD unit. In both cases, there was no evidence for H/D scrambling in the aromatic ring or the Me group.…”